Frequency Modulation Multiplexing for Simultaneous Detection of Multiple Gases by use of Wavelength Modulation Spectroscopy with Diode Lasers

Modulation frequency multiplexing provides a straightforward method, analogous to television or radio broadcasting, for performing simultaneous detection of multiple gases by use of wavelength modulation spectroscopy with diode lasers. When fiber-optic coupled lasers are used, our approach guarantees that all beams transit the same optical path and impinge on the same detector. Each laser is modulated at a different frequency and the detector output is processed by a set of lock-in amplifiers, one for each laser, to measure the absorbance encountered by each laser.     

An Optically Narrowed Diode Laser for Rb Saturation Spectroscopy

Abstract

Diode laser linewidths have been reduced by a factor of up to 20 000 using the technique of resonant optical feedback. In this method, the laser frequency also locks optically to a confocal cavity, greatly improving the passive frequency stability. For the first time, such an optically narrowed diode laser has been used to obtain high-resolution Doppler-free spectra of the D₂ line of ⁸⁵Rb and ⁸⁷Rb at 780 nm.     

可调谐半导体激光吸收光谱测温谱线选择

可调谐半导体激光吸收光谱(Tunable Diode Laser Absorption Spectroscopy,TDLAS)作为非接触光学测量手段,在燃烧诊断、推进系统研发中应用广泛,而吸收谱线对的选择是采用TDLAS技术进行燃气温度测量的基础和关键一步。在扫描波长-直接吸收法测量H_2O温度的实验中,首先系统地研究了谱线选择的基本原则和实现步骤,对选择原则中各指标的量化进行了重点分析;然后对中心频率在7000～7500 cm~(-1)范围内的水分子吸收谱线进行研究和筛选;最后结合数值模拟进行分析,选择了7022. 7091,7444. 3707 cm~(-1)和7185. 5962,7444. 3707cm~(-1)两对谱线,为TDLAS温度测量系统设计提供依据。     

质谱法测量OLED封装材料的气体渗透率

本文介绍了质谱法渗透率测量系统和测量方法,利用该系统测量了水蒸汽、O2和CO2等气体对PET塑料薄膜和环氧树脂薄膜的渗透率,对所获得的实验结果进行了分析;结果表明PET塑料薄膜的水蒸汽渗透系数为1.76×10-6cm2/s,O2和CO2的渗透系数分别为4.5×10-9,2.25×10-8cm2/s,DG-4型环氧树脂的水蒸汽、O2和CO2的渗透系数分别为1.4×10-6,4.85×10-11和8.5×10-10cm2/s。实验结果表明PET塑料和环氧树脂的水和氧的渗透率很大,不适合作为长寿命OLED的封装材料;本文还讨论了所使用的质谱法渗透率测量系统存在的问题,以及该系统的改进方法。     

基于TDLAS技术的空间真空环境下温度测量技术研究

可调谐二极管激光吸收光谱(TDLAS)技术可用于气体温度的高精度快速测量,但目前TDLAS技术研究一般集中在正压范围内,真空环境下该技术的应用研究较少.空间真空环境由于压力极低,传统的接触式温度测量技术存在众多不确定性因素.本文从热力学温度定义出发,提出并分析了TDLAS技术测量空间真空环境下痕量气体分子振-转温度的可能性和精度.同时以C2H2分子1535.393nm和1535.432nm两条吸收谱线为例,分析了TDLAS技术测量气体分子振-转温度的方法和精度.分析结果表明即使压力达到1.0× 10-3 Pa,如果在实验中选取吸收强度大的谱线对,同时增加有效吸收光程,可以得到比较理想的吸收信号,实现气体分子振-转温度的测量.     

Tunable Diode Laser Absorption Spectroscopy of Carbon Monoxide Around 2.35 microm

Novel GaInSbAs/GaSb multiple-quantum-well lasers operating near room temperature have been successfully used for tunable diode laser absorption spectroscopy in the vicinity of 2.35 mum. Continuous current tuning over a more than 150-GHz frequency range has been realized. Direct absorption measurements have been carried out on the R, R, R, and R lines of carbon monoxide. Traces of carbon monoxide at the level of 0.3 part in 10(6) in volume at 100 Torr could be detected by the low-frequency wavelength-modulation technique and an astigmatic multipass cell. These results show a potential use of these diode lasers in portable low-cost trace-pollutant sensors.     

Quantitative Analysis of Trace Moisture in N(2) and NH(3) Gases with Dual-Cell Near-Infrared Diode Laser Absorption Spectroscopy

This paper demonstrates our optical measurement system based on near-infrared tunable diode laser absorption spectrometry and reports the results of trace moisture determination in nitrogen and ammonia gases. A near-infrared InGaAsP distributed feedback diode laser operating at room temperature was employed as the optical source. We used a dual-cell detection strategy to cancel common mode noise from the diode laser and remove the effect of the residual moisture absorption in the beam path outside the sample cell. We also used this method to successfully eliminate the interfering absorption of matrix gas molecules such as NH(3). The detection limit of H(2)O absorption of 4 ppb in nitrogen and 12 ppb in ammonia was obtained using a single-pass absorption cell of only 92 cm in length and the average results of 10 scan measurements. This system has characteristics of both the high sensitivity and capability of in situ and real-time measurement.     

YAG Laser End and Side Pumped by a Laser Diode

A combined end and side pump approach for a YAG laser pumped by a laser diode is proposed. The theoretical analysis of the total pump efficiency of the end and side pump module is presented. A laser-diode-pumped YAG laser is successfully demonstrated by use of this pump configuration. The experimental pump threshold is 81.2 mJ, the maximum output is 4.4 mJ, and the optical efficiency is approximately 3.1% for Q-switched operation of the YAG laser.     

红外吸收光谱（NDIR）检测混合气体中二甲醚含量分析法

利用非分光红外吸收光谱法（NDIR）,采用中红外光源（波长：2．5—25μm）和主要包括样品气气阻、样品泵、红外吸收池和电路模块技术建立了混合气体中二甲醚气体成分光谱检测系统,并使用该系统对混合气体中的二甲醚气体成分进行了测量,得到了1．0×10^-2的检测灵敏度。整个光谱检测系统具有很好的光谱分辨率、选择性以及测量灵敏度,适用于各种混合气体中二甲醚气体成分的检测。     

Measurement of Non-Stationary Gas Flow Parameters Using Diode Laser Absorption Spectroscopy at High Temperatures and Pressures

The layout of an absorption spectrometer with diode lasers for contactless measurement of the temperature and water-vapor concentration in gas flows with mixture pressures of up to 3 atm and temperatures of 300–2000 K has been designed. The technique is based on the rapid tuning of the radiation wavelength of two lasers, the registration of the absorption lines of water molecules that are located in the tuning range, and the fitting of the experimental absorption spectra by theoretical ones that have been simulated using spectroscopic databases. The original components of the spectrometer and different algorithms of the processing of experimental spectra are described. The performance of the spectrometer and processing methods were tested in the laboratory with a cuvette at a pressure of 1 atm and temperatures of 300–1500 K. The different processing algorithms give a reasonable coincidence of data on hot zone parameters that were obtained by the method of diode laser absorption spectrometry, and the temperature that was measured using standard sensors. The designed layout of the spectrometer passed the first tests on the T-131 experimental stand at the TsAGI (Central Aerohydrodynamics Institute).     

A Compact Laser System for Remote Measurements by Laser-Induced Breakdown Spectroscopy Based on a Nd:YAG Laser with Self-Phase Conjugation

Technical Physics Letters - A compact laser system based on a Nd:YAG laser with self-phase conjugation for remote analysis of substances by laser-induced breakdown spectroscopy at a distance of not...     

Phase Recovery in Interferometers by Optothermal Diode Laser Modulation

Abstract

A technique is described for the frequency modulation of a diode laser based on the optothermal effect. It is shown that it is possible to generate the frequency modulation with a minimum of power modulation. A frequency shift of approximately 1 GHz per mW of optothermal pump power was achieved in practice. The power modulation was about 7% of that observed when injection current modulation was used to generate a similar frequency shift. The optothermal frequency modulation technique was applied in a phase recovery scheme for a fibre interferometer based on pseudo-heterodyne signal processing.     

Tunable Diode Laser Spectroscopy for Industrial Process Applications: System Characterization in Conventional and New Approaches

Tunable diode laser spectroscopy (TDLS) can only be successfully implemented if a number of system characterization procedures and critical parameter measurements can be made accurately. These include: application of a wavelength/frequency scale to the signals recovered in time; measurement of the frequency dither applied to the laser; measurement of the relative phase between the laser power modulation and frequency modulation; determination of the background amplitude modulation for normalization purposes and measurement of required cross broadening coefficients for the host/target gas mixtures. Easy to implement, accurate and low-cost systems and procedures for achieving these are described and validated below. They were developed for two new approaches to TDLS measurements, viz the residual amplitude modulation (RAM) technique and the phasor decomposition (PD) method, but are equally applicable to all forms of TDLS. Following full system characterization using the new techniques, measurements of the absolute transmission function of the 1650.96 nm absorption line of methane over a wide range of concentration and pressure were made using the RAM technique. The close agreement with theoretical traces derived from HITRAN data validated the entire approach taken, including the system characterization procedures. In addition, measurements of a wide range of gas concentration and pressure were made by curve fitting theoretical traces to the measured transmission functions obtained using a variety of operating conditions. Again, the low errors confirmed the validity of the new methods and the system characterization/measurement procedures described here.     

采用组合透镜阵列准直半导体激光器线阵

为了满足半导体激光器线阵的远距离应用要求,需要对激光束进行准直处理.提出了一种由垂直双半圆柱透镜组合阵列构成的准直器,采用光线追迹的方法推导了激光束通过准直器的传输方程,分析了光线出射角与透镜阵列参数之间的关系,得出了准直器的最优设计参数,然后在zemax-EE非序列模式下仿真了此准直器的三维效果图以及探测器成像效果,得到的激光光斑接近于矩形,非相干照度集中在中央区域,并且经过准直器后的发散角大约为3 mrad.设计的准直透镜可以同时压缩快慢轴的激光束发散角,制作简单,安装方便.